Pathology 17

• Transmission of bacteria can occur through various routes such as spreading of microbes, during transmission, the infectious agent escapes from the host or reservoir of infection, may live in the environment until find suitable host, enter the new host, perform its action, escape and find new host.
• Routes of transmission can be vertical or horizontal, examples of vertical transmission include mother to infant through breast milk, passage through birth canal, and trans placental.
• Examples of horizontal transmission include direct contact, indirect contact through fomites, oral, airborne, vector borne, and zoonotic.
• Microbes can enter through mucous membranes, open wounds, or abraded skin.
• Examples of bacteria that can cause infections through these routes include Staphylococci or MRSA, Leptospira, Neisseria, and others.
• Fomites are inanimate objects contaminated by an infected individual, examples include medical equipment, towels or clothes, environmental surfaces, and others.
• Oral transmission can occur through contaminated food or water, examples include Salmonella, Cholerae, Escherichia coli, Campylobacter.
• Airborne transmission involves the transfer of pathogens via very small particles or droplet nuclei, it occurs through breathing, coughing, sneezing, medical procedures such as suctioning, bronchoscopy, dentistry, inhalation anesthesia.
• Adherence or attachment in bacterial pathogens involves surface proteins such as pili and fimbria.
• Pilus has a shaft composed of a protein called pilin.
• Virulence factors are molecules produced by pathogens that cause disease in the host.
• Virulence is the ability of an organism to cause infections and it depends on the type of virulence factors and the infective dose.
• Pilus depolymerizes and enhances strong adhesion between bacteria and host.
• Bacteria enter the host only for nutrition and a good environment to survive, they do not really want to kill the host because if they do so, they will not have good food and shelter.
• Most pathogens are well adapted to the host and show mild or self-limited infections like fever, headache, rashes etc.
• Virulence factors can be categorized as adherence or attachment, invasion, escape phagocytosis, toxins, and iron acquisition.
• Pili are thin, protein tubes originating from the cytoplasmic membrane.
• The end of the shaft is the adhesive tip which attaches to receptor in cell and establishes initial contact.
• Pilus is present only in Gram-negative bacteria.
• Some pathogens who are poorly adapted to the host will produce life-threatening virulence factors.
• Portals of entry of pathogens include the skin, conjunctiva, mucous membrane, respiratory tract, gastrointestinal tract, genitourinary, placenta, and parenteral (bite, wounds, cut).
• Not all strains of any species are pathogenic, for example, only certain strains of E. coli secretes diarrhoea-causing toxins.
• Vector borne transmission involves the transfer of pathogens from one location to another by living organisms, examples include mosquitoes for Dengue and Malaria, fleas for plague, rodents for Leptospirosis, and ticks for Lyme disease or borreliosis.
• Zoonotic transmission is the transmission from animal to human, it can be through direct and indirect contact, examples include Leptospira, Campylobacter, and Anthrax.
• Vertical transmission can occur from mother to infant through breast milk, passage through birth canal, and trans placental.
• Cytotoxins cause structural damage and an inflammatory response, examples include E.coli cytotoxins, some types of venom, chemotherapy.
• Hair like structures on the surface of the bacteria, present in both Gram - positive and Gram - negative bacteria are known as pyogenes.
• Invasion is an important process in infectious diseases, it is the entry of bacteria into host cells, avoid host defense, find nutrient rich niche area and live happily without any competition from other bacteria.
• Exotoxins are secreted proteins released during the exponential phase, they are antigenic and elicit antitoxins, mostly heat labile.
• Adhesins are adhesion proteins found in the cell wall of various bacteria that bind to specific receptor molecules on the surface of host cells and enable the bacterium to adhere intimately to that cell in order to colonize and resist physical removal.
• Endotoxins are lipopolysaccharides present in the outer membrane of Gram-negative bacteria, released on cell lysis and small amount during replication, they are heat stable and contain side chain oligosaccharides and core polysaccharides, including Lipid A.
• Enterotoxins are toxins that target the intestine, examples include Staphylococcus aureus and E.coli enterotoxins, causing food poisoning and travellers diarrhea.
• Bacterial toxins are toxic substances secreted by bacteria that damage the host tissues and also disable the immune system.
• Neurotoxins damage nerves, the Central Nervous System, the Peripheral Nervous System, and can lead to intellectual disability, persistent memory loss, epilepsy, dementia.
• A glycocalyx is a polysaccharide layer found outside the cell wall, it is a virulence factor because it prevents phagocytosis, protects from engulfment by macrophages, contains water, allows bacteria to adhere to smooth surfaces such as prosthetic implants and catheters.
• Competing for iron and other nutrients, generally, bacteria compete for nutrients by synthesizing specific transport systems or cell wall components capable of binding limiting substrates and transporting them into the cell.
• Phagocytosis is the process where white blood cells engulf and digest microorganisms.
• Neisseria gonorrhoeae, Neisseria meningitidis, Haemophilus influenzae, and Borrelia burgdorferi are examples of bacteria that cause specific and non-specific diseases.
• Acid Fast Mycolic acid and Peptidoglycan Fragments (Muramyl Dipeptides) are PAMPs for Acid Fast Bacilli.
• Components of the first line of defense include phagocytic cells such as neutrophils, monocytes, and macrophages, innate lymphoid cells like natural killer (NK) cells, and polymorphonuclear leukocytes.